Acids & Bases

Acids vs. Bases ACIDS Turn litmus red Taste sour Feel “burny” Highly reactive Water soluble Ionic compounds Start with “H” BASES Turn litmus blue Taste bitter Feel slippery Highly reactive Water soluble Ionic compounds May end with “OH”

Arrhenius Theory Svante Arrhenius – Nobel Prize winner in 1903 for Chemistry for his work with solutions. An acid is a substance that produces H + ions when it’s dissolved in water. A base is a substance that produces OH - ions when it’s dissolved in water. Seemed to fit – all the acids started with H + and OH - was in many bases!

Arrhenius’ Problem The problem with Arrhenius’ theory of acids and bases was that there were groups of salts that acted as acids or bases when they were dissolved in water. Salts are simple ionic compounds that may not contain hydrogen or hydroxide ions in their composition. So Arrhenius theory was later discarded… “My revenge shall be swift and sweet!” Arrhenius died in 1927 before any revenge could be exacted.

Brønsted-Lowry Theory Johannes Brønsted and Thomas Lowry came up with a better theory for describing acids and bases in An acid is any molecule or ion that can give up a hydrogen ion (H+). A base is any molecule or ion that can combine with a hydrogen ion. “An acid is a proton donor, I do say!” “And a base…a proton acceptor old chap!”

Conjugate Acids & Bases According to Brønsted-Lowry, every base has a corresponding acid and every acid has a corresponding base. WHAT?!?!?! Basically, when a acid donates its proton (H + ), its leftovers can now accept a proton back. And a base will accept the proton and become something that can give that extra proton away. Look at the equations below: HCl + H 2 O  H 3 O + + Cl - Acid + Base  CA + CB NH 3 + H 2 0  OH - + NH 4 + Base + Acid  CB + CA

Strong & Weak ACIDS A strong acid will completely dissociate – fall apart into ions – when placed in water. This is known as ionization. A weak acid will only partially dissociate or ionize. Some of it will remain in tact while some of it will fall apart. BASES A strong base will completely dissociate – fall apart into ions – when placed in water. A weak base will only partially dissociate or ionize. Some of it will remain in tact while some of it will fall apart.

Strength & Dissociation

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